*
    margin 0
    padding 0

.header 
    height 100px
    background-color green
    h1 
        font-weight 700
        font-style 26px
        color blue

.footer
    background pink
    height 100px

main
    display flex
    nav,div,aside
        height 500px
        width 200px
        background-color yellow
    nav
        background-color grey
    aside
        background-color red
    div
        // flex 1  //主要元素
        width calc(100% - 400px)
